Originally Posted by
silverloaf
on a freshly made blade you will start to see the beginnings of this line rather quickly, especially larger/heavier blades. friction is the main culprit with moisture being his little buddy that aids in the oxidizing of that line, leaving the thing darkened like it is in contrast to the rest of the blade. even humidity in the air will do it, if it sits unattended for a length of time, once the friction between blade and scales creates little scratches (you may not even notice them unless you look intentionally for them in raking light). the darkening is made far worse in cases like sharptonn pointed out, putting away a blade damp is asking for all kinds of issues. leaving that blade sitting after putting away damp will exacerbate those issues. if you dry the blade well before putting away you will still see this line over time but it may not appear dark at all, just matte compared to rest of blade.